Gasoline producing process



Jan. 13, 1970 o. STINE ET AL GASOLINE PRODUCING PROCES S Filed Nov. 5, 1967 /V l/E/V TORS; Laurence 0. Stine B Jack B. Poh/enz fmw 47 7 0 NEYS United States Patent 3,489,673 GASOLINE PRODUCING PROCESS Laurence O. Stine, Western Springs, and Jack B. Pohlenz,

Arlington Heights, Ill., assignors to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Nov. 3, 1967, Ser. No. 680,501 Int. Cl. Cg 37/04 U.S. Cl. 208-73 8 Claims ABSTRACT OF THE DISCLOSURE Process for the enhanced production of high octane gasoline in a catalytic cracking process wherein a hydrocarbonaceous feed oil and a recycled heavy cycle oil are catalytically cracked over regenerated cracking catalyst and a recycled hydrotreated cycle oil is employed to strip a portion of the oil off partially deactivated catalyst while the hydrotreated cycle oil is being catalytically cracked over the partially deactivated catalyst.

This invention relates to the production of high octane gasoline. More specifically, this invention relates to the production of gasoline from heavy hydrocarbonaceous feeds by a route which results in higher octane number and higher yields. Still more specifically, this invention relates to the upgrading of a normally refractory byproduct stream from a catalytic cracking process which is then converted to a gasoline of high quality under catalytic cracking conditions especially selected to optimize the conversion of the upgraded stream. Furthermore, this invention relates to a J-factor analysis of the upgrading step to correlate this analysis with catalytic cracking conversion conditions to optimize the yield and octane improvement obtained when the upgraded byproduct stream is converted to gasoline.

In one of its embodiments, this invention relates to a process for producing gasoline which comprises the steps: (a) catalytically cracking a hydrocarbonaceous feed and a heavy cycle oil as defined in step (h) hereinbelow by cocurrent contact with a regenerated fluid cracking catalyst in a dilute phase riser cracking zone to form first reaction products and thereby partially deactivated cracking catalyst; (b) separating at least :a portion of the first reaction products from the partially deactivated catalyst; (c) passing the partially deactivated catalyst into a fluidized dense phase bed of catalyst; (d) catalytically cracking a hydrotreated light cycle oil as defined in step (k) hereinbelow by contact with the dense phase bed of partially deactivated cracking catalyst to form second reaction products and to partially strip first reaction products from the partially deactivated catalyst; (e) separating at least a portion of the second reaction products (g) recovering a gasoline from the commingled product of step (f); (h) recovering a heavy cycle oil from the commingled product of step (f) and returning the heavy cycle oil to step (a); (i) recovering a light cycle oil having an average boiling point above the average boiling point of the gasoline of step (g) and below the average boiling point of the heavy cycle oil to step (h), said light cycle oil being rich in aromatics, the major single type of aromatic being J-12; (j) hydrotreating the light cycle oil by contact with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics but convert the types of aromatics such that the major type of aromatic is J-8; and (k) recovering the hydrotreated light cycle oil from step (3') and returning ice It has been known for many years that heavy charge stocks such as gas oil, vacuum gas oil, coker gas oil, etc., may be cracked in the presence of a cracking catalyst to produce light hydrocarbons (C4 which are rich in olefins) and high octane gasoline (C to about a 430 F. end point which is recovered as a primary product). In addition, most catalytic crackers are operated at conditions such that heavy product oil is obtained from the reaction zone. The reaction zone product is introduced into a fractionator and separated therein. Typically, the fractionator has an upper side out well and a lower side cut well and is operated to remove gasoline and light hydrocarbons overhead, the heavy cycle from the lower side out well (material produced from the lower well maintained at about 550 F.), a bottoms or slurry oil (material produced from the column bottoms maintained at about 700 F.) and. a refractory light cycle oil from the upper side cut Well (material produced from the upper well maintained at about 440 F.). Generally, the heavy cycle oil is recycled to the catalytic cracking zone while the slurry oil is clarified whereupon it may be cracked or recovered as a fuel oil. The refractory light oil generally is not recycled to the catalytic cracking zone since it is very refractory and is not readily cracked further. It has also been taught to hydrogenate this refractory oil to improve its cracking characteristics. For example, U.S. Patent 2,671,754 shows the separate desulfurization and hydrogenation of this refractory oil. Other published articles have shown general improvement in cracking characteristics of cycle oils by hydrogenation as, for example, shown in the Chemistry of Petroleum Hydrocarbons, vol. 3, chapter 52, pages 333 to 334. However, the prior art has failed to recognize the ultimate improvement in high quality gasoline, the manner in which the hydrogenation should be carried out of optimize the hydrotreating step in relation to the subsequent cracking of the hydrotreated product and the conditions under which the hydrotreated oil should be catalytically cracked in order to optimize the gasoline producing reaction in terms of yield and octane number. The present invention provides for the hydrotreating of the light cycle oil in a specific manner and the subsequent cracking of said light hydrotreated cycle oil to optimize its conversion to gasoline. An analytical technique has been developed which permits the characterization of various types of aromatics in a hydrocarbon mixture called a J-factor analysis. It is in essense a mass spectrometer analysis employing a low ionizing voltage technique. The ionizing chamber is maintained at a potential of about 7 volts and the vaporized hydrocarbon mixture is introduced therein. Compounds more saturated than aromatics such as parafiins have to step (d).

an ionization potential of about 10 volts and these saturated compounds will not be observed on the mass spectrum since they are not ionized. The mass spectrum reveals molecular ion peaks which correspond to the molecular weight of the aromatic compound which permits characterization of these aromatics by means of the general formula: C H2 J where J is the J-factor. The following table shows the relationships between the J- factor and the type of aromatic.

TABLE I Type of aromatic hydrocarbon: J-factor No. Alkyl benzenes and benzene 6 Indanes, tetralins 8 Indenes 10 Alkyl naphthlenes and naphthlene 12 Acenaphthenes, tetrahydroanthracene 14 Acenaphthalenes, dihydroanthracenes 16 Anthracenes, phenanthrenes 18 Using this J-factor analysis in characterizing the hydrotreating step of this invention, allows for the optimum hydrotreatment of said refractory light cycle oil to efliciently produce high octane gasoline in a subsequent catalytic cracking step. It must be born in mind that there is a relationship between the hydrotreating step and the subsequent catalytic cracking step such that the light cycle oil is hydrotreated to the proper extent and then catalytically cracked at the proper operating conditions. Under appropriate circumstances, the present invention allows the complete conversion of the refractory light cycle oil into high quality gasoline.

It is an object of this invention to render a light cycle oil derived from a catalytic cracker readily susceptible to further cracking.

It is another object of this invention to catalytically crack hydrotreated cycle oil over a partially deactivated catalytic cracking catalyst thereby optimizing the gasoline producing reactions therefrom.

It is still another object of this invention to utilize a hydrotreated light cycle oil to partially strip entrained oil oil? partially deactivated catalyst before the partially deactivated catalyst is regenerated in a catalytic cracking process.

These and other objects will become apparent in the light of the following detailed description.

The accompanying drawing shows a schematic flow scheme for a preferable embodiment of the present invention in which separate catalytic cracking zones are employed to convert the hydrotreated light cycle oil and the mixture of fresh feed stock and recycle heavy cycle oil. As shown therein, a fresh feed stock is introduced into conduit 3 where it is commingled with recycled heavy cycle oil flowing in conduit 2 and the resulting mixture flows into conduit 3 whereupon it mixes with hot regenerated cracking catalyst flowing in conduit 4. The feed stock, heavy cycle oil and catalyst are mixed therein and flow upward through riser and into cyclone 7 contained within reaction chamber 6. The catalyst is composed of fine particles such that it acts as a fluid bed. Therefore, the catalyst will flow down through conduit 4 under the influence of gravity and will flow cocurrently along with the feed stock and heavy cycle oil up through conduit 5 in a dilute phase wherein the reactions occur. The fresh feed and heavy cycle oil react in conduit 5 under the catalytic influence of the cracking catalyst to produce a wide variety of products including light hydrocarbons, gasoline, refractory light cycle oil, heavy cycle oil, slurry oil, and coke. The coke generally is formed on the fluid catalyst particles. The partially deactivated catalyst having coke deposited thereon is separated from the other reaction products by means of cyclone 7. Although the schematic flow scheme shows one cyclone, it is contemplated that a bundle of series and/ or parallel flow cyclones will be employed to attain an efiicient separation between the other reaction products and the partially deactivated catalyst with coke thereon. The separated reaction products pass through cyclone 7 and out conduit 11 where they flow through conduit 13 and out of reaction chamber 6. These separated reaction products flow through conduit 13 and into fractionator 14. Fractionator 14 is operated to produce at least 4 and possibly 5 product streams therefrom. A hydrocarbon stream containing light hydrocarbons and gasoline is withdrawn overhead from fractionator 14 through conduit 15 where it flows through cooler 16 and into separator 40. Vapor phase light hydrocarbons composed mainly of C to C hydrocarbons are withdrawn from separator 40 through conduit 41. Light phase gasoline is withdrawn from separator 40 through conduit 42 whereupon it is recovered as the desired principal prodnot of the process. Heavy cycle oil is withdrawn from fractionator 14 through a lower side cut well and out conduit 2 where it is returned to conduit 3 being mixed therewith with feed stock. Slurry oil is withdrawn from the bottom of fractionator 14 through conduit 37 where it is introduced into settler 38. The clarified slurry oil is withdrawn through conduit 39 where it may be used as fuel oil or it may be recycled back to flow conduit 3 for further cracking and conversion. Under certain operations no slurry oil will be produced. A refractory light cycle oil is withdrawn from fractionator 14 through an upper side cut well and out conduit 17 where it flows into conduit 20 and into hydrotreating reaction zone 21. Hydrogen from sources defined hereafter flows through conduit 19 and is commingled with the refractory light cycle oil and the mixture flows through conduit 20 and into zone 21. The hydrotreating step is preferably carried out by loading the hydrotreating catalyst into a fixed bed within zone 21. The material to be hydrotreated passes through the fixed bed of catalyst maintained at hydrotreating conditions. An efliuent is withdrawn from reaction zone 21 through conduit 22 which is cooled and introduced into separator 23. The eflluent is separated into a normally liquid hydrotreated product and a normally gaseous stream. The normally gaseous stream is withdrawn from separator 23 through conduit 24 where it flows through recycle compressor 25 and through conduit 26 where it is commingled with fresh hydrogen flowing in conduit 18 to produce a combined hydrogen gaseous stream which is then passed through conduit 19, and then back to reaction zone 21 as described hereinabove. If desired, a portion of the normally gaseous stream may be vented to maintain hydrogen purity although this is not generally necessary. The normally liquid product stream is withdrawn from separator 23 through conduit 27 where it may be flashed or stripped to remove dissolved gases such as hydrogen and hydrogen sulfide although if desired this step may be omitted. In some instances, a portion of this oil (normally liquid product) is used as a hydrotreated fuel oil in which case it may be withdrawn through conduit 33 by opening valve 34. The hydrotreated light cycle oil is returned to a catalytic cracking zone through conduit 27 where it is introduced at a lower portion of reaction chamber 6 and passes through distributor 32 to disperse the hydrotreated light cycle oil in the dense bed of partially deactivated catalyst contained therein. The hydrotreated light cycle oil is catalytically cracked in the dense bed contained within reaction chamber 6 to form reaction products including gasoline, light hydrocarbons and coke. A portion of these reaction products are carried into cyclone 9 contained within reaction chamber 6 which is employed to separate any remaining partially deactivated catalyst from these separated reaction products. The separated reaction products are withdrawn from cyclone 9 through conduit 12 where they are commingled with reaction products flowing in flow conduit 11 to produce the total reaction products separated and withdrawn through conduit 13. It should be noted that cyclones 7 and 9 contain diplegs 8 and 10 respectively to seal the cyclones into the dense bed of catalyst contained within reaction chamber 6. It should be noted by using the particular flow scheme employed herein the hydrotreated light cycle oil only contacts partially deactivated catalyst. This is considered an important feature of the present invention since the partially deactivated catalyst has had some of its higher activity level reduced such that when it converts the hydrotreated light cycle oil there is produced a better quality product in higher yields.

If additional outside charge stock is available which is refractory in nature, it may be introduced into this flow scheme through conduit 35 where it mixes with the refractory light cycle oil prior to entering the hydrotreating reaction zone. Generally, a charge stock would be introduced at this point only because it is diificult to catalytically crack relative to the feed stock and the heavy cycle oil. In this event, the outside charge stock is hydrotreated to render it more easily crackable while optimizing the J-factor of said stock to optimize the subsequent conversion thereof in the catalytic cracking zone over partially deactivated catalyst to produce high quality gasoline in high yields.

The fluid cracking catalyst introduced into reaction chamber 6 along with feed stock and heavy cycle oil via riser 5 is separated from the reaction products therefrom in cyclone 7. The partially deactivated catalyst flows down through dipleg 8 into a dense bed of partially deactivated catalyst contained in the lower portion of reaction chamber 6. The partially deactivated catalyst continues to flow downwardly through the dense bed of catalyst finally passing through distributor 32 and into stripper 28. Generally, steam is introduced into stripper 28 through conduit 36 where it countercurrently contacts the descending fluidized partially deactivated cracking catalyst to strip entrained oil off the catalyst. The partially deactivated catalyst has been contacted with the hydrotreated light cycle oil in the dense bed above distributor 32, and it has been found that the hydrotreated light cycle oil is effective in stripping a portion of the heavier components entrained on the catalyst thereoif thereby helping to strip the catalyst and reduce the required stripping steam. As a result of this particular flow scheme, it has been found that the steam required to strip the remaining entrained oil olf the descending catalyst through the stripper is markedly reduced. As a result, the size of the stream flowing in conduit 36 is much less than it would be in the absence of the particular flow scheme shown herein. It should be recognized that the catalyst contained in the dense bed above distributor 32 in reaction chamber 6 is partially deactivated, that is, it has had the deposition of fresh coke due to cracking in riser 5. It hasalso been found that the catalytic cracking of a hydrotreated light cycle oil over the partially deactivated cracking catalyst results in enhanced cracking to desired products in contrast with contacting the hydrotreated light cycle oil directly with fresh regenerated catalyst. Although it is not exactly understood why, it is believed that freshly regenerated catalyst contains a number of highly acidic sites which are passified when the feed stock and heavy cycle oil are cracked thereover. Therefore, the catalyst contained in the lower portion of chamber 6 will not tend to tear up the hydrotreated light cycle oil as much as freshly regenerated catalyst would which will produce more gasoline and less coke and light hydrocarbons thereby increasing the yield of high octane gasoline. The partially regenerated catalyst flows downward through stripper 28 and into regenerator vessel 29 wherein the catalyst is regenerated by burning a portion of the coke thereoff. Air is introduced into regenerator vessel 29 through conduit 30 where the oxygen contained therein reacts with a portion of the coke on the catalyst to produce carbon oxides. An effluent gas comprising nitrogen and carbon oxides is withdrawn from regenerator vessel 29 through conduit 31. The catalyst that has now been regenerated contained within regenerator 29 is withdrawn therefrom through conduit 4 to begin the cycle over again.

It is to be understood, of course, that there are numerous variations in the basic catalytic cracking process in terms of fluidized beds, fixed beds, position of the regenerator and reactor vessels, etc., and it is intended that all of the basic catalytic cracking processing schemes be included in the process of the present invention.

One preferable alternate embodiment utilizing the process of this invention involves elimination of the heavy cycle oil recycle wherein the entire cycle oil stream is hydrotreated and such hydrotreated cycle oil is returned to the dense bed of cracking catalyst via conduit 27 shown in the drawing. Thus, in this alternate embodiment there is no material flowing in conduit 2. Hydrotreating of the entire cycle oil will render it more crackable and if desired, the cracking severity in the reaction zone can be increased to minimize the volumetric flow rate of the cycle oil flowing in conduit 11.

There are a large number of catalysts suitable for use in the catalytic cracking process such as amorphous silicaalumina, silica-magnesia, silica-zirconia, acid-activated clay, crystalline catalysts including faujasite, dispersed in a silica-containing inorganic oxide matrix, mordenite-containing catalysts either dispersed in a silica-containing matrix, an alumina-containing matrix or used in the pure form, pure faujasite, etc. Preferred cracking catalysts for use in the present process are amorphous silica-alumina having concentrations of from about 10 to about 40 weights of alumina and from 90 to about 60 weights of silica, and faujasite dispersed in a silica-containing inorganic oxide matrix. When using the faujasite in silicacontaining matrix catalysts, it is preferred that the faujasite concentration be from about 2 to about 20 weight percent, and the sodium content of the faujasite be reduced to a major extent, preferably having a sodium content less than about 2 weight percent of the faujasite. Suitable cations to activate the faujasite include hydrogen, polyvalent cations, including calcium, magnesium, etc., and rare earth metal cations.

Typical catalytic cracking operating conditions comprise reaction temperatures of from about 800 F. up to about 1050 F., regenerator temperatures of from about 1000 F. up to about 1300 F., pressures of from about atmospheric to about 50 p.s.i.g., oil to catalyst weight ratios above about 1 to about 10 and combined feed ratios (ratio of fresh feed plus heavy cycle oil divided by fresh feed) of from about 1.1 to about 2.0. These variables, some of which are independent and some of which are dependent, are adjusted to maintain conversions per pass to gasoline of from about 30% up to about 70% and in some instances up to about The hydrotreating catalyst is preferably sulfur resistant, that is it possesses hydrogenation activity in the presence of sulfur compounds. A preferable catalyst comprises a silica-alumina support having at least one metal or metal compound from Group VI of the Periodic Table and one metal or metal compound of Group VIII of the Periodic Table. Especially preferable are those catalysts having tungsten and/or molybdenum along with nickel or cobalt on silica-alumina supports. Other supports such as alumina, silica-zirconia, silica-magnesia, faujasite, mordenite, inorganic oxide matrix containing at least one crystalline aluminosilicate, etc., are also suitable. Other metals are also suitable as for example noble metals such as platinum or palladium. These latter noble metal catalysts are generally satisfactory without the presence of a group VI metal contained thereon.

The hydrotreating conditions employed in hydrotreater 21 such as temperature, pressure, LHSV, hydrogen to oil ratio, etc., are selected to convert the refractory light cycle oil to a product having as the major single type of aromatic hydrocarbon present J-8 as defined hereinabove. It has been found that the refractory light cycle oils having L12 as the major single type of aromatic hydrocarbon are not cracked as readily as the feed stock components which will cause the build-up of light cycle oil J-l2 components when the light cycle oil is recycled. The above hydrotreating process variables are accordingly controlled to maximize the Il2 to J-8 conversion reactions therein. It is generally preferable to maintain pressure, LHSV, and hydrogen to oil ratio constant and vary the temperature to maximize the J-12 to J8 conversion. The initial choice of all these variables depends to a large measure on the charge stock. Suitable pressure ranges are from about 400 to about 2000 p.s.i.g. with 600 to 1200 being preferable. Suitable LHSV is from 0.5 up to about 20, with 3 to 10 being preferable. Suitable hydrogen to oil mole ratios are from about 2 to about 20, with 5 to 15 being preferable. When these conditions are selected, the temperature is adjusted to maximize the I-l2 to J-8 conversion. It is expected that temperatures within the range of from about 500 F. up to about 850 F. will be employed. The most preferred way to obtain the proper operating conditions is to select the independent variables, conduct a J-factor analysis on the stream flowing in conduit 20 and in conduit 27 and adjust the temperature to attain the maximum conversion of L12 to L8. If the operating conditions are too severe, the J-12 will be converted to J-6 or the aromatics will be saturated. This has the undesirable effect of increasing hydrogen consumption and reduces the octane number of the gasoline produced when the hydrotreated light cycle oil is subsequently:

catalytically cracked. If the hydrotreating conditions are not severe enough, there will be little improvement in the refractory nature of the light cycle oil which will make it difiicult to convert to gasoline. When properly hydrotreated, this material is readily catalytically cracked and the actual cracking characteristics and yield of gasoline produced therefrom is optimized by ctalytically cracking this hydrotreated light cycle oil over a partially de activated catalyst as described hereinabove.

In order to obtain high quality gasoline, at conversions of 100%, the hydrotreating conditions may have to be adjusted to account for a foreign charge stock which may be introduced into conduit 35. The nature of this foreign charge stock in contrast to the nature of the refractory light cycle oil will have to be considered in the selection of the final variables to be employed in hydrotreater 21. It has been found that when the hydrotreated light cycle oil has been catalytically cracked over partially deactivated catalyst, according to the process of the present invention, a gasoline will be produced having I-6 as the major single type of aromatic present therein, a preferable motor fuel. It has also been found that the unconverted hydrotreated light cycle oil which has been catalytically cracked (unconverted being defined as having a boiling point in the range above the boiling point range of gasoline) contains J-12 as the major single type of aromatic present therein. This means that the catalytic cracking zone in which the hydrotreated light cycle is converted over partially deactivated cracking catalyst has converted the hydrotreated light cycle oil boiling above gasoline into a gasoline having L6 as the major single type of aromatic and an unconverted heavy material boiling above gasoline having J-12 as the major single type of aromatic. For this reason, any unconverted hydrotreated light cycle oil is readily recycled and cracked to extinction by recycling it back to the hydrotreating step again since the I-12s are then reconverted to J-8s. This will allow the complete conversion of the light cycle oil into gasoline boiling range materials or lighter.

It is now apparent that the present invention permits the conversion of gas oil feed stocks to gasoline and lighter in amounts of 90% or higher. Indeed, conversions of up to 100% are possible with the process of this invention providing the slurry oil is also cracked. In this sense, this overall process has the same advantages as hydrocracking to produce gasoline from gas oil, a feat which up until now has been impossible. Furthermore, the light hydrocarbons produced in conduit 41 are rich in olefins which permits alkylation with parafiins to produce high octane isoparafiins which can be added to the total gasoline yield. When this is practiced, the present process in combination with alkylation will produce a most desirable high octane motor fuel having as its main components alkyl benzene aromatics and isoparaffins. Another advantage of the present process relative to the hydrocracking process is that the catalytic cracking and the hydrotreating steps are carried out at relatively low pressures when compared to hydrocracking thus minimizing capital investment and operational Problems.

It is difficult to characterize the split points between the light refractory cycle oil and the gasoline and heavy cycle oil by commonly observed physical characteristics since the split point varies depending upon the initial feed stock, operating characteristics, and desired yields, etc. In some cases, the end point of the light cycle oil will vary from 550 F. or less to as much as 750 F. or more.

The most preferable manner of characterizing the light cycle oil and the heavy cycle oil is the place from which each originates. As used herein, heavy cycle oil is that material withdrawn from the lower side cut well in the catalytic cracking main column fractionator, said well being maintained at about 550 F. The gasoline from the catalytic cracker may be characterized by the boiling point range or end point, the end point generally being Within the range of from about 350 F. up to about 450 F. and typically about 430 F. The light refractory oil is therefore the material boiling between the gasoline and the heavy cycle oil. The light refractory cycle oil is derived from an upper side cut well in the main column fractionator 14, said well being maintained at about 440 F. The above side out well temperatures are for fractionator pressures of from about 10 to about 15 p.s.i.g. and if the pressure is outside this range, the well temperature will, of course, be shifted.

Suitable feed stocks for introduction into conduit 1 constitute gas oils such as ordinary gas oil, vacuum gas oil, coker gas oil, etc. Suitable charge stocks for introduction into conduit 35 are those hydrocarbonaceous feeds derived from other sources which are more difficult to catalytically crack that the feed stock material. Sources of such outside charge stock for introduction into conduit 35 comprise other catalytic cracking operations, purchased cycle oils, etc.

The following example is presented to further illustrate the process of the present invention.

EXAMPLE Equipment is arranged substantially as shown in the accompanying drawing. A mixture of atmospheric and vacuum gas oil is introduced into the catalytic cracking reaction zone through conduit 1. The riser reactor zone 5 is maintained at a temperature of about 900 F. and pressures of about 19 p.s.i.g. The combined feed ratio is about 1.2. A refractory light cycle oil is withdrawn from conduit 17 from fractionator 14 in an amount of about 20% of the volume of fresh feed where it flows into hydrotreater 21. The hydrotreater is maintained at a pressure of about 800 p.s.i.g., a liquid hourly space velocity of about 2, a hydrogen circulation rate of about 3000 s.c.f./bbl. and a temperature of about 700 F. The entire normally liquid product recovered from separator 23 is recycled back through conduit 27 into the dense bed of partially deactivated cracking catalyst contained within reactor chamber 6. It is estimated that under continuous operation of this process conversions of the gas oil feed stocks will be in excess of We claim as our invention:

1. A process for producing gasoline which comprises the steps:

(a) catalytically cracking a hydrocarbonaceous feed and a heavy cycle oil as defined in step (h) hereinbelow by cocurrent contact with a freshly regenerated fluid cracking catalyst in a dilute phase riser cracking zone to form first reaction products and partially deactivated cracking catalyst;

(b) separating at least a portion of the first reaction products from the partially deactivated catalyst;

(c) passing the partially deactivated catalyst into a fluidized dense phase bed of partially deactivated catalyst;

(d) catalytically cracking a hydrotreated light cycle oil as defined in step (k) hereinbelow by Contact with the dense phase bed of partially deactivated cracking catalyst to form second reaction products and to partially strip the partially deactivated catalyst;

(e) separating at least a portion of the second reaction products from the cracking catalyst;

(f) commingling at least a portion of the first and the second reaction products;

(g) recovering a gasoline from the commingled product of step (f);

(h) recovering a heavy cycle oil from the commingled product of step (f) and returning the heavy cycle oil to step (a);

(i) recovering a light cycle oil having an average boiling point above the average boiling point of the gasoline of step (g) and below the average boiling point of the heavy cycle of step (h), said light cycle oil being rich in aromatics, the major type of aromatic being 1-12;

(j) hydrotreating the light cycle oil by contact with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics but convert the types of aromatics such that the major type of aromatic is 1-8; and

(k) recovering the hydrotreated light cycle oil from step (j) and returning at least a portion of said hydrotreated light cycle oil to step (d).

2. The process of claim 1 further characterized in that the entire hydrotreated light cycle oil recovered in step (k) is returned to step (d).

3. The process of claim 1 further characterized in that a charge stock is introduced into the hydrotreating reaction zone of step (j) along with the light cycle and at least a portion of the hydrotreated product therefrom is returned to step (d).

4. In a catalytic cracking process for the production of high octane gasoline wherein hydrocarbonaceous feed and a recycled heavy cycle oil are catalytically cracked by cocurrent contact with a freshly regenerated fluid cracking catalyst in a riser reaction zone maintained at cracking conditions to produce reaction products and partially deactivate the cracking catalyst, the partially deactivated catalyst is separated from a portion of the reaction products, the separated reaction products are fractionated into portions comprising high octane gasoline, a light cycle oil and a heavy cycle oil, the heavy cycle oil is recycled to the riser reaction zone, and the partially deactivated catalyst is collected in a dense bed thereof, stripped to remove entrained oil thereoff and returned to a regenerator reaction zone to regenerate the catalyst, the improvement which comprises hydrotreating the light cycle oil and returning the hydrotreated light cycle oil to the dense bed of partially deactivated catalyst to catalytically crack the hydrotreated light cycle oil and aid in stripping the entrained oil off the catalyst.

5. A process for producing gasoline which comprises the steps:

(a) catalytically cracking a hydrocarbonaceous feed oil by cocurrent contact with a freshly regenerated fluid catalytic cracking catalyst in a dilute phase riser cracking zone to form first reaction products and partially deactivated cracking catalyst;

(b) separating at least a portion of the first reaction products from the partially deactivated catalyst;

(c) passing the partially deactivated catalyst into a fluidized dense phase bed of partially deactivated catalyst;

(d) catalytically cracking a hydrotreated cycle oil as defined in step (j) hereinbelow by contact with the dense phase bed of partially deactivated cracking catalyst to form second reaction products and to partially strip the partially deactivated catalyst;

(e) separating at least a portion of the second reaction products from the cracking catalyst;

(f) commingling at least a portion of the first and second reaction products;

(g) recovering a gasoline from the commingled product of step (f);

(h) recovering a cycle oil having an average boiling point above the boiling point of the gasoline of step (g), said cycle oil being rich in aromatics, the major type of aromatic being 1-12;

(i) hydrotreating the cycle oil by contact with a hydrotreating catalyst in the presence of hydrogen at hydrotreating conditions in a reaction zone to retain a major portion of the aromatics but convert the types of aromatics such that the major type of aromatic is 1-8; and,

' (j) recovering the hydrotreated cycle oil from step (i) and returning at least a portion of said hydrotreated cycle oil to step (d).

6. The process of claim 5 further characterized in that the entire hydrotreated cycle oil recovered in step (i) is returned to step (d).

7. The process of claim 5 further characterized in that a charge stock is introduced into the hydrotreating reaction zone of step (i) along with the cycle oil.

8. In a catalytic cracking process for the production of high octane gasoline wherein a hydrocarbonaceous feed is catalytically cracked by cocurrent contact with a freshly regenerated fluid cracking catalyst in a riser reaction zone maintained at cracking conditions to produce reaction products and partially deactivate the cracking catalyst, the partially deactivated catalyst is separated from a portion of the reaction products, the separated reaction products are fractionated into portions comprising a high octane gasoline and a cycle oil, and the partially deactivated catalyst is collected in a dense bed of partially deactivated cracking catalyst, stripped to remove entrained oil thereoff and returned to a regenerator reaction zone to regenerate the cracking catalyst, the improvement which comprises hydrotreating the cycle oil and returning the hydrotreated cycle oil to the dense bed of partially deactivated catalyst.

References Cited UNITED STATES PATENTS 3,065,166 11/1962 Hennig 20867 DELBERT E. GANTZ, Primary Examiner ABRAHAM RIMENS, Assistant Examiner US. Cl. X.R. 208-68, 72, 

